I. Field of the Invention
This invention relates generally to electrical safety switches, and more specifically to the design of a position sensitive switch assembly which is specifically constructed for use in environments where any electrical arc or spark cannot be tolerated.
II. Description of the Prior Art
There are a wide variety of applications for a switch arrangement of the type to be described herein. For example, in grain storage and handling applications, it is often times convenient to use conveyor belt systems for transporting loose grain. However, because the dust particles emanating from dried grain mix with air, the mixture is potentially highly explosive and combustible.
Conveyor systems also generally utilize devices for detecting an overload or jam condition. For example, there is disclosed in the Schlagel U.S. Pat. No. 3,952,864 an arrangement utilizing a low-travel Microswitch-type mechanical switch cooperating with a cam which is effective to sense the travel of a conveyor pulley which occurs during an overload or jam situation. The switch is electrically connected in circuit with the conveyor drive motor so that when the switch toggles, power is removed from the motor.
While this arrangement may be altogether suitable for use with conveyor systems in environments where there is no concern over explosion, in those applications where such a risk is high, it is totally unsuitable because of the possibility of the generation of an electrical arc or spark in an overload situation.
The Schmeck et al U.S. Pat. No. 3,066,789 also discloses a jam detector for a conveyor belt system in which mercury-type switches are employed to sense the relative position of a conveyor drive or idler pulley. In the Schmeck arrangement, the mercury switches are mounted in a tipped orientation so that their contacts are normally open. A sudden translation of the conveyor pulley occasioned by a jam will cause one or the other of the switches to become closed and this action results in a de-energization of the conveyor drive motors.